Plate tectonic theory, a milestone in twentieth-century science, has been instrumental in advancing our understanding of Earth’s geological history, the formation of its surface features, and its earthquake movement. Geophysicist W. Jason Morgan—who introduced plate tectonics at a 1967 meeting of the American Geophysical Union—will discuss how the theory came about, highlighting both the role of ocean exploration in the 1950s and 1960s and early observations of seafloor spreading and ocean magnetic anomalies. He will also touch on the advances made in understanding Earth’s movements since the development of space geodesy instruments and technologies.